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Geologic Time
Principle of Earth Science
GEOL 1212
7/7/2015
The Geologic Time Scale
●  Recognize the relationship among the units—era, epoch, and period—into
which the geologic time scale is divided.
●  Illustrate the vast diversity of life that has been present on Earth over time
by using the geologic time scale.
●  Summarize how scientists study Earth’s past environment and diverse lifeforms by examining different types of fossils (including molds, casts,
petrified fossils, preserved and carbonized remains of plants and animals,
and trace fossils).
●  Explain how Earth’s history has been influenced by catastrophes (including
the impact of an asteroid or comet, climatic changes, and volcanic activity)
that have affected the conditions on Earth and the diversity of its lifeforms.
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Why is it important to understand
Geologic Time?
Many geologic events and processes occur
through very long durations of time and may
occur at rates that are so slow as to be nearly
imperceptable.
Extra Credit: How old is Earth?
Why is it important to understand
Geologic Time?
●  The Geological time scale is a record of the life forms
and geological events in Earth’s history.
●  Scientists developed the time scale by studying rock
layers and fossils world wide.
●  Radioactive dating helped determine the absolute
divisions in the time scale.
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Divisions of Geologic Time
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